1. Field of the Invention
This invention relates to a triplet lens using plastic lens elements.
2. Description of Related Art
Since plastic lenses are lighter in weight than glass lenses and are produced at low cost by the technique of injection molding, recently the number of products which use plastic lenses in part of the optical system have been increasing.
Also for triplet lenses, lenses that use the combination of a glass positive lens element with a high index of refraction closest to the object side with a plastic biconcave lens element, and a plastic biconvex lens element, as proposed in published Japanese Laid-Open Patent Application No. 62-183420, are well known as lenses for use in low cost compact cameras.
However, with the triplet lens referred to in the published Japanese Laid-Open Patent Application No. 62-183420, the angle of view is approximately 60.degree. at most, and if the angle is enlarged to be greater than this, problems in performance occur because a large negative distortion and lateral chromatic aberration cannot be avoided and flatness of the image field cannot be maintained without using expensive glass with a high index of refraction, which is unsatisfactory.
It is an object of the present invention to provide a low cost triplet lens using plastic lenses in which the chromatic aberration off-axis is satisfactorily corrected while obtaining an F number approximately between 4 and 4.5 and an angle of view between approximately 60.degree. and 70.degree..